Equivalent of Underscore _.pluck in pure JavaScript

Question

I'm trying to recreate the Underscore pluck function using pure JS. However, I keep getting an array of undefineds being returned, instead of the actual values from the properties of the objects in an array.

Checking another thread here I found that you could reproduce it in jQuery with the following code...

$.pluck = function(arr, key) {      return $.map(arr, function(e) { return e[key]; })  } 

...however I am having difficulty just reproducing this in pure JS. I tried the following, however this is just returning an array of undefineds for me.

var pluck = function(arr,key){   var newArr = [];   for (var i = 0, x = arr.length; i < x; i++){     if (arr[i].hasOwnProperty(key)){       newArr.push(arr[i].key)     }   }   return newArr; } 

So, the goal would be the following, except instead of using the underscore _.pluck, just use a JS function name, eg. var pluck = function(arr,key){...}

var Tuts = [{name : 'NetTuts', niche : 'Web Development'}, {name : 'WPTuts', niche : 'WordPress'}, {name : 'PSDTuts', niche : 'PhotoShop'}, {name : 'AeTuts', niche : 'After Effects'}]; var niches = _.pluck(Tuts, 'niche');  console.log(niches);  // ["Web Development", "WordPress", "PhotoShop", "After Effects"] 

Could someone steer me in the right direction?

Answer 1

In ES5:

function pluck(array, key) {   return array.map(function(obj) {     return obj[key];   }); } 

In ES6:

function pluck(array, key) {   return array.map(o => o[key]); } 

Answer 2

You can do it with the native JavaScript .map():

Array.prototype.pluck = function(key) {   return this.map(function(object) { return object[key]; }); }; 

edit — modifying built-in prototype objects should be done with care; a better way to add the function (should you be OK with the idea of doing so in general) would be with Object.defineProperty so that it can be made non-enumerable:

Object.defineProperty(Array.prototype, "pluck", {     value: function(key) {         return this.map(function(object) { return object[key]; });     } });